Update: disappointment - priority inbox sections haven't been updated. They're still limited to 2 by the UI, and the new UI still doesn't expose "with label, in inbox" that's been possible for years by modifying the HTML on the page. The Gmail server clearly supports this, so it's a shame they haven't implemented a UI for it. I hope this doesn't break the hack people have been using to get 4 sections with messages only from the inbox...